1. Field of the Invention
This invention relates to a precision parallel translation system suitable for use, for example, with an exposing device used in the process of production of integrated circuits for effecting transfer-printing of a pattern formed on a mask on a resist film formed on a wafer, to position the wafer placed on a table with respect to the mask with a high degree of precision.
2. Description of the Prior Art
With advances made in the development of integrated circuits in recent years, circuit patterns printed on the wafers are becoming more and more miniscule, making it necessary to increase the precision with which positioning of the mask and the wafer relative to each other is effected when a circuit pattern is printed by transfer-printing on the wafer. For example, when the circuit pattern has a line width of 1 .mu.m, a high precision of an allowance of below .+-.0.1 .mu.m is required in positioning the mask and the wafer relative to each other.
Proposals have been made to use a precision parallel translation system in which an X-Y table for fine movement is arranged on an X-Y table for rough movement, for the purpose of effecting high precision positioning.
The X-Y table for rough movement of the aforesaid precision parallel translation system comprises a first X (or Y) table arranged on a base for reciprocating movement by the operation of a screw transmission, and a first Y (or X) table arranged on the first X table serving as a base for reciprocating movement by the operation of a screw transmission. The X-Y table for fine movement comprises a second X (or Y) table supported on a pair of plate springs mounted parallel to each other on the Y table for reciprocating movement in the direction of thickness of the plate springs by energization of an electromagnet positioned against an end face, and a second Y (or X) table supported on a pair of plate springs parallel to the X table for reciprocating movement in the direction of thickness of the plate springs by energization of an electromagnet positioned against an end face.
In effecting precision positioning of a wafer with respect to a mask by using a precision parallel translation system of the aforesaid construction, the wafer is placed on the second Y table and moved by means of the X-Y table for rough movement to a position below the mask to position the former precisely with an allowance of about .+-.several .mu.m.about.10 .mu.m with respect to the latter. Thereafter a current flowing to the electromagnet of the X-Y table for fine movement is adjusted to effect precision positioning of the wafer with respect to the mask.
Some disadvantages are associated with the precision parallel translation system of the aforesaid construction. The construction in which the X-Y table for rough movement and the X-Y table for fine movement are piled in a stack increases the height of the system (the elevation of the surface on which the wafer is placed from the level of the base). In addition, the bulk of the system becomes inordinately large as compared with the size of a wafer. The position of the center of gravity of the system as a whole is remote from the drive shaft for the X-Y table for rough movement, so that errors would tend to occur in the translation of the X-Y table and the system would be sensitive to influences exerted from outside, such as vibration. Thus the precision achieved by this system in positioning the wafer with respect to the mask is on the order of .+-.0.5 .mu.m.